1. Field of the Invention
The present invention generally relates to an electronic appliance, a recharging method, and a recharging apparatus. More specifically, the present invention is directed to an electronic appliance employing a secondary cell such as a rechargeable battery as a power source thereof, and a method/apparatus for recharging the secondary cell.
2. Background of the Invention
Usually, electronic appliances such as portable CD (compact disk) players and tape recorders use secondary cells, e.g., Ni-Cd batteries and Li-Ion batteries as power sources.
There are the below-mentioned recharging methods of recharging apparatus with respect to these secondary cells.
As the first recharging method, when a secondary cell is mounted on the recharging apparatus, the recharging operation to the secondary cell is commenced and also a time lapse is measured from the commencement of this recharging operation by the internal timer during the recharging operation. When a preselected time has passed after the recharging operation was commenced, this recharging operation is accomplished. In other words, according to this first recharging method, the recharging operation is carried out for a predetermined time period for the secondary cell connected to the recharging apparatus, irrelevant of the discharging conditions of this secondary cell.
In another conventional recharging method, a voltage of a secondary cell is detected during the recharging operation to acquire the end timing of this recharging operation. That is, according to the conventional recharging method, since the voltage of the secondary cell is increased to a certain peak voltage and thereafter becomes stable at a voltage lower than the peak voltage by .DELTA.V, this voltage variation is detected and used to stop this recharging operation.
However, these conventional recharging methods have the following problems.
In the first recharging method for continuously performing the recharging operation for a predetermined time, there are some possibilities that the secondary cell set to the recharging apparatus is recharged for a predetermined time even when this secondary cell has not been fully discharged. This first recharging method may produce such a problem that the secondary cell is readily brought into the overcharging state. If the secondary cell is brought into the overcharging state, then the recharging cycle lifetime of the secondary cell is lowered.
To prevent such an overcharging state in the first recharging operation, a so-called "trickle charging" operation is acceptable, whereby the recharging operation is carried out under low currents and for a long time period. However, in the case of the execution of this trickle charging operation, a lengthy charging time is necessarily required. As a result, when the secondary cell is quickly wanted for use, this secondary cell and the electronic appliance using this secondary cell cannot be utilized until the trickle charging operation is completed.
In the latter recharging method where the voltage drop from the peak voltage by .DELTA.V is detected to obtain the recharging operation stop timing, the above-described overcharging state may be prevented. However, since the various control circuits for detecting the voltages of the secondary cell and for controlling the cell based on the detected voltage required, the hardware construction would become complex, and the manufacturing cost of the recharging apparatus would be increased, and further a bulky recharging apparatus would be constructed. Specifically, this second recharging method may cause such a serious problem when the recharging apparatus operated under the second recharging method attempted to be assembled into a compact portable electronic appliance.
Furthermore, when the more correct recharging operation is realized while preventing the secondary cell from being overcharged, not only the voltage detection at the terminal voltage of the secondary cell is required, but also the temperature/recharging current detections of this secondary cell are required. As a consequence, the overall circuit arrangement of such a recharging apparatus would be more complex.